U.S. Pat. No. 3,667,721 generally describes an annular blowout preventer for closing and sealing on an open hole, a casing, drill pipe, tubing, or kelly in which the inner surface of the upper housing is a spherical surface.
The present invention is directed to an improved annular blowout preventer in which the overall height is shorter, the hydraulic volume required to actuate the preventer is reduced by at least 50% thereby reducing the size of the required hydraulic actuating system, the closing time of the blowout preventer is reduced by about 50%, and the cost of the blowout preventer is substantially reduced.